Method of generating an alternating current of variable frequency



Feb. 16,1926. 1,573,367

H. DE F. ARNOLD. ET AL METHOD OF GENERATING AN ALTERNATING CURRENT OFVARIABLE FREQUENCY Original Fiied Nov. 12, 1917 /nve/2f0rs-: Ham/dD./Irno/c/. John P. Minion.

374W. Arr

Patented Feb. "16, 1926.

1,573,367 PAJENT HAROLD DE FOREST ARNOLD, OF MAPLEWOOD, NEW JERSEY, ANDJOHN P. MINTON,

OF WHITE PLAINS, NEW YORK, ASSIGNORS TO WESTERN ELECTRIC COMPANY, IN-CORPORA'IED, OF NEW YORK, Y., A CORPORATION OF NEW YORK.

METHOD OF GENERATING AN ALTERNATING CURRENT OF VARIABLE FREQUENCY.

Original application filed November 12, 1917, Serial No. 201,565, nowPatent No.'1,426,807, dated August 22, 1922. Divided and thisapplication filed September 8, 1920. Serial No. 408,843.

To all whom it may concern:

Be it known that we, HAROLD DE FOREST ARNOLD and JOHN PRESTON MINTON,citizens of the United States, residing at Maplewood,

in the county of Essex, State of New Jersey,

and White Plains, in the county of VVestchester, State of New York,respectively, have invented certain new and useful Improvements inMethods of Generating an Alternating Current of Variable Frequency, ofwhich the following is a full, clear, concise, and exact description.

This invention relates to oscillation generators of a type in which thefrequency can be caused to vary cyclically and continuously over aselected range, and is a division of U. S. patent to Arnold and Minton1,426,- 807, August 22, 1922.

The above-mentioned patent discloses an application of this invention ina system in which it is particularly adapted to be used. The inventionthere disclosed is a method of and a system for testing the comparativeefliciency of telephone transmitters orreceivers. In this machine methodof testing transmitters, as distinguished from what maybe designated thevoice method, the vibrating element of the transmitter, or receiver, isacoustically actuated by a mechanical means which embodies the presentinvention. The invention disclosed in the prior patent makes use of asource, for example, a telephone receiver, the sound emit ted from whichis conducted into the transmitter in such a manner as to exclude, as faras possible, resonant or interference effects of the outside air, to theend that the sound energy may be transmitted from the source to theinstrument under test in an efficient manner, and in such a manner as tosimulate, as closely as poss1ble, the characteristic ,modes of speechtransmission.

The source, in this case a telephone receiving instrument, shouldcorrespondingly be made to simulate in its function and mode ofoperation, the human agency of speech or voice. It is well known thattelephone currents produced by speaking into a transmitter. are verycomplex and may be considered as made up of currents of variousfrequencies extending over the acoustic range. In order to duplicateactual working conditions, even approximately, by comhinations ofmechanical elements, there are obviously presented formidablediliiculties. A special form of generator is required for energizing thereceiver which actuates the element under test.

In the invention of the prior patent this generator is caused to supplycurrent which continuously and cyclically varies in frequency over theimportant part of the voice frequency range, thereby casting apparatusat all frequencies which are most important in speech. Ordinarydiaphragms, as is well known, are not equally responsive to forces ofall frequencies. Hence, if in the above testing system a current havinga variable frequency is supplied to the receiver, its diaphragm, havinga non-uniform frequency response, would give rise to more intense soundsat some frequencies than at others. This is not important in casecomparative tests are being made, since all of the elements underinvestigation are tested under like conditions, although if it isdesired to investigate the frequency response characteristic of theelement under test, or if it seems desirable. for any other reason, thereceiver diaphragm may be actuated by well-known means so as to giverise to equally intense sounds at all frequencies. I

The present invention resides in an oscillation generator adapted to beused in a testing system similar to that disclosed in the said priorpatent, and in the method of causingthe frequency of the generator tovary cyclically and continuously over a se lected range, although theinvention is considered as having a much broader application than isindicated by this use.

The primary object of the invention is to provide an oscillationgenerator for producing a continuously and cyclically varying frequency.Secondary objects of the invention are, to provide an oscillationgenerator capable of producing oscillating currents of a continuouslyand cyclically varying frequency over the range of audible frequencies,

and especially over that range of audible frequencies which is necessaryfor telephone apparatus to transmit efiiciently in order to producespeech, and to vary the oscillation frequency of a generator having anoscillation circuit comprising capacity, over a selectedrange, by meansof cyclically varying said capacity. Further objects of the 11;-

vention.

For an illustration of one of the forms embodying the invention andsuitable for carryingout the method, reference is made to theaccompanying drawing, in the single figure of which is shown'theapplication of the invention to above.

In the drawing is shown a machine testing system for testing element 1,which is t illustrated as a telephone transmitter. The

diaphragm of transmitter 1 is acoustically actuated by source 2, hereshown as a telephone receiver, and which may be of the usual magnetictype, and in the circuit of V which is a means, embodying the invention,

for producing in the diaphragm of the re ceiver vibrations having acontinuously and cyclically varying frequency. In this circuit thegenerator G supplies current to the receiver 2. This generator is shownas one form of the audion type in which the grid and plate circuits areinductively coupled by means of inductances 3 and 4, the oscillationcircuit including inductances 3, 4, the

primary winding of transformer 7 and the capacity .5. An audion ty e ofoscillation generator isshown, althoug any other type,

inwhich the frequency of oscillations depends on the inductance andcapacity constants of an oscillation circuit, may be used. In the t pehere shown, the frequency of the'oscillation depends upon the values ofthe inductances 3, 4 and the transformer primary and the capacity 5. Itis the essence of'the invention to vary the frequency of the generatorcontinuously. and cyclically between selected limits incontradistinction to a step-by-ste variation which would, in this case,be un esirable. This ma be done by varying cyclically either one otheconstants, inductance and capacity, which enter into the frequencyequation of the oscillation circuit. For the purpose'of this uously1invention it is proposed to vary the capacity 5. This ma be accomplishedby continrotating the movable element of avaria e condenser by means ofa constant speed motor 19 connected to the movable element of thecondenser by means of shaft 20., Condensers capable of being operated inthe manner described are well known to those versed in the art and it isnot considered necessary to disclose aspecific embodiment in thisspecification.

The currents delivered by the generator may be amplified by theamplifier A before they are sent to the repeating element comavebeendescribed. The average voltage of the current supplied to thereceiver 2,

observed by means of I voltmeter 6,- is maintained. onstant. f

the system briefly described" morass:

The input circuit of amplifier A is shown as deriving its electromotiveforce from the output circuit of the oscillator G by means of thetransformer 7, and the receiver circuit is similarly coupled with theoutput circuit of amplifier A, although in either case direct couplingmay be used.

A voltmeter 18 may be provided across 7 the terminals of thetransmitter 1. In circuit with the transmitter 1 is provided a suitableelectrical load which may be made up, asshown, of series resistance orinductances 9 and shunt condensers 10 having suitable values to simulatethe impedanc'e of any desired length of telephone cable.

Direct current for the transmitter 1 is supplied by the battery 11through the coils 12 and 13 inductively related to the coils 14. Incircuit with the coil'14 are two rectifiers 15 and 16 connected inopposition, so as to rectify the alternating current. The ammeter 17measures the rectified current. By means of voltmeter 18 and ammeter 17the energy used in the transmitter circuit may be calculated inaccordance with well known principles.

From the above description it will be accordingly a current mayconceivably be causedito. cyclically vary even though there is no.orderly sequence in the consecutive periods. The word uniformly herelimits the term to the case in which there isa definite and constantperiod. Further, the term c 'clically alone as used herein does not impy any particular mode of variation but concerns merely the end productsof the periodic variation. In the present case, the word continuouslylimits the conception to a cyclical'change in which there is a change infrequency from each instant of time to every other instant of time,however sli ht the interval of time may be. The alternating currentdelivered by the transmitter 1 to its lead circuit'9 and 10 may beobserved b means of the measuring instrument 17 6n account of its massthe natural period .of the needle of this instrument is great ascompared with the period of impressedcurrent impulses. Accordingly, itis unable to follow the minute variations of the current and is given asubstantially steady-deflection which is a measure. of theaverageefi'ectof the variable currents. For the purpose of comparison,other transmit ters orreceivers, .01 com onentparts thereof, maybeSflbfl mted, 6 alterna ing Out- -cal relation .rather than that .oftime, and y put ilreacli case being compared with an arbitrarily chosenstandard. It is thus possible to determine whether or not the devicesunder test meet the necessary requirements as to efficiency throughoutthe acoustic range.

The features of the invention which are believed to be novel have beenpointed out above as applied in a specific system for which it isparticularly well adapted. It should be understood, however, that theinvention is equally well adapted to be used in other systems, in whichit is desired to make use of a source of alternations, the frequency ofwhich continuously and cyclically varies, and further that the inventionis not necessarily limited to generators adapted to produce variationsin frequency of the order used in telephone circuits since it is wellknown that oscillators of the audion type have been built capable ofoscillating withfrequencies much below audio frequency and-withafrequency of many millions,

nor to a generator of the audion type, as has been pointed out.

What is claimed is:

' 1. The method of operating an oscillator which is adapted to generatea continuous wave of a single frequency and which includes a frequencydetermining oscillation circuit, whichcomprises cyclically andcontinuously varying the tuning of said oscillation circuit.

' 2. The method which comprises generating an alternating current, andsimultaneously continuously and cyclically varying the frequency of thecurrent as generated within the acoustic range.

3. An oscillation generator comprising an audion tube, an oscillationcircuit for determining the frequency of said generator, and means forvarying the resonance of.said

circuit whereby said generator is adapted to supply current uniformlyand recurrently varying in frequency.

4. In combination, means for continuously producing a substantially puresine wave, comprising a frequency determining oscillation circuitincluding a variable condenser which has a rotatable electrode forvarying its capacity, and means for continuously and cyclically varyingthe capacity of said condenser by uniformly and continuously rotatingsaid element.

5.'An oscillation generator of variable frequency, comprising incombination an electron discharge device which includes a cathode, ananode, and an impedance controlling element, a source of continuousspace current connected to said anode, coupled input and output circuitsrelated to said discharge device, reactive circuit means associated withsaid circuits and constituting therewith a resonant circuit, and meansfor continuously and cyclically varying the constants of said reactivecircuit.

6. In combination, an oscillation generator comprising a highlyevacuated containing vessel, an electronemitting cathode, an anode, andan impedance-controlling element, coupled circuits related to saidlastmentioned element, a frequency-controlling condenser of variation,to constitute, with said coupled circuits, a resonant circuit, and meansfor continuously and cyclically varying the capacity of said condenser.

In witness whereof, I hereunto subscribe my name this 17th day of AugustA. D., 1920.

HAROLD DE FOREST ARNOLD.

In witness whereof, I hereunto subscribe my name this 21st day of AugustA. D.,

JOHN P. MINTON.

